A metallic glass is excellent in such properties as strength, hardness, wear resistance and corrosion resistance. Therefore, it is expected to be used in various fields.
However, despite having such excellent properties, the metallic glass has disadvantages such as poor workability and poor weldability. Thus, in order to expanding the field of application of a metallic glass, it is important to establish a technique of welding between two metallic glasses. Furthermore, in view of fabricating an actual device component or the like, it is also necessary to establish a technique of joining between a metallic glass and a practical crystalline metallic material. In this connection, there have been reported research results in which an explosion bonding method, a friction welding method, or a fusion welding method, is employed as joining means therefor.
However, in cases where a welding method designed to melt a joining region is employed, a metallic glass and a crystalline metal are melt-mixed together in a melt region formed on a butt interface therebetween to cause deterioration in glass-forming ability. And thus, consequently, a brittle intermetallic compound is caused to form, which makes it impossible to obtain a joined body having sufficient weld strength.
Considering the above problem, there has been reported a research result in which a welding method is employed which is designed to scan a high-energy beam, such as an electron beam or a laser beam, over a butt interface between a metallic glass and a crystalline metal, wherein the high-energy beam used as a heating source for welding is capable of forming a sharp penetration shape and suitable for local rapid heating and cooling, so that rapid heating and rapid cooling can be achieved while suppressing melt-mixing of two butted members in a welding region, as disclosed in the following Non-Patent Document 1
The report also discloses that an adequacy of welding between a metallic glass and a crystalline metal depends on whether a composition of a melt zone formed around an interface therebetween falls within a composition range which allows a TTT (Time/Temperature/Transformation) curve for crystallization of the melt zone to be set on a long-time side relative to a cooling curve during the high-energy beam welding.
The inventors of this application previously proposed a welding method designed to scan a high-energy beam in a position shifted from a butt interface between a metallic glass and a crystalline metal toward the metallic glass, so as to allow a component composition of a melt zone formed around the butt interface during welding to have a glass-forming ability, as disclosed in the following Patent Document 1.
This method is intended to shift the scanning position of the high-energy beam from the butt interface between the metallic glass and the crystalline metal toward the metallic glass in such a manner that an amount of fused metallic glass becomes greater than that of fused crystalline metal in the melt zone to allow a component composition of the melt zone to fall within a range of composition ratios having a glass-forming ability.
Non-Patent Document 1: Materials Transactions, Vol. 42, No. 12 (2001), pp. 2649-2651
Patent Document 1: JP 2006-88201A